metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: tan, buff, or light brown due to iron oxide staining; Luster: dull to vitreous; Crystal structure: granular/non-foliated; High specific gravity around 2.65.
- Hardness
- 7 on Mohs scale
- Color
- tan, buff, or light brown due to iron oxide staining
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, buff, or light brown due to iron oxide staining; Luster: dull to vitreous; Crystal structure: granular/non-foliated; High specific gravity around 2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to heat and pressure during regional metamorphism. This specific specimen has been rounded into a 'cobble' through fluvial (river) or glacial transport processes.
Uses & applications
Used as a durable construction aggregate, decorative garden stone, and historically for stone tools due to its conchoidal fracture.
Geological facts
Quartzite is so hard it will scratch glass and is resistant to chemical weathering. It is often tougher than its parent sandstone, meaning it survives long trips down rivers which is why it is often found as smooth river stones.
Field identification & locations
Identify by its extreme hardness and sugary, crystalline texture on a fresh break. Commonly found in riverbeds, glacial tills, and mountainous regions like the Appalachians or the Alps.
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